8.3 Thermografische Verfahren
Filtern
Dokumenttyp
- Vortrag (133)
- Zeitschriftenartikel (69)
- Beitrag zu einem Tagungsband (51)
- Posterpräsentation (31)
- Preprint (4)
- Sonstiges (2)
- Buchkapitel (1)
- Dissertation (1)
Schlagworte
- Thermography (108)
- Thermografie (51)
- NDT (41)
- Additive Manufacturing (39)
- Additive manufacturing (35)
- Super resolution (34)
- Additive Fertigung (29)
- Laser thermography (22)
- Zerstörungsfreie Prüfung (19)
- Laser (15)
- Laser Powder Bed Fusion (15)
- Process monitoring (14)
- DLP (13)
- DMD (13)
- Inspection (13)
- Internal defects (13)
- Non-destructive testing (13)
- In situ monitoring (11)
- Infrared thermography (11)
- Laser Thermography (10)
- GFRP (9)
- In-situ monitoring (9)
- ZfP (9)
- Active thermography (8)
- FEM (8)
- Joint sparsity (8)
- Künstliche Bewitterung (8)
- L-PBF (8)
- Laser metal deposition (8)
- Laser powder bed fusion (8)
- Flying line thermography (7)
- Image resolution (7)
- In-situ Monitoring (7)
- Nondestructive testing (7)
- PBF-LB/M (7)
- ProMoAM (7)
- VCSEL array (7)
- Virtual wave (7)
- 1d laser (6)
- 3D Druck (6)
- Defect detection (6)
- High-power laser (6)
- Laser Metal Deposition (6)
- Laser array (6)
- VCSEL (6)
- Wind turbine rotor blades (6)
- Kunststoffe (5)
- LMD (5)
- Lock-in Thermography (5)
- Machine Learning (5)
- Optical tomography (5)
- Photothermal (5)
- Prozessüberwachung (5)
- Pulsed thermography (5)
- Selective laser melting (SLM) (5)
- Standardisierung (5)
- Super Resolution (5)
- 2D model (4)
- Additive manufacturing (AM) (4)
- CFRP (4)
- Canny approach (4)
- Compressed sensing (4)
- Crack detection (4)
- Data reconstruction (4)
- Direct energy deposition (4)
- Emissivity (4)
- Flash thermography (4)
- Flat bottom holes (4)
- GFK (4)
- Heat accumulation (4)
- Infrared Thermography (4)
- Laser scanning (4)
- Lock-in thermography (4)
- Material testing (4)
- Normung (4)
- Notches (4)
- Numerical modelling (4)
- Passive thermography (4)
- Photothermal imaging (4)
- Pulse thermography (4)
- Schichtdickenbestimmung (4)
- Super-resolution (4)
- Thermal conductivity (4)
- Thermal wave (4)
- Wind energy (4)
- 3D printing (3)
- Aktive Laserthermografie (3)
- Aktive Thermografie (3)
- Analytical model (3)
- Artificial weathering (3)
- Beton (3)
- Betonbeschichtung (3)
- Compressed Sensing (3)
- Convolutional Neural Networks (3)
- Defect reconstruction (3)
- Delamination (3)
- Direct Energy Deposition (3)
- Eingeschlossene Defekte (3)
- Laser Pulver Auftragsschweißen (3)
- Laser beam melting (LBM) (3)
- Laser powder bed fusion (L-PBF) (3)
- Laserthermografie (3)
- Machine learning (3)
- Multispectral thermography (3)
- Neural network (3)
- Nondestructive Testing (3)
- Oberflächenschutzsystem (3)
- Opaque materials (3)
- Optische Tomografie (3)
- Photothermal super resolution (3)
- Photothermisch (3)
- Projektor (3)
- Representative specimens (3)
- Residual Stress (3)
- Rotorblatt (3)
- Semitransparent (3)
- Subsurface defects (3)
- Super-Resolution (3)
- TES (3)
- Temperature emissivity separation (3)
- Thermal history (3)
- Thermographie (3)
- Ultrasonics (3)
- AISI 316L (2)
- Ablösungen (2)
- Active thermal imaging (2)
- Anlage (2)
- Barker codes (2)
- Bauthermografie (2)
- Beton-Oberflächenschutzsysteme (2)
- Composite materials (2)
- Computed Tomography (2)
- Concrete (2)
- Cracks (2)
- Deep learning (2)
- Deep unfolding (2)
- Defect Detection (2)
- Digital light processing (2)
- Dimension reduction (2)
- Elastic net (2)
- FEM simulations (2)
- FFT (2)
- Faserverbundwerkstoffe (2)
- Fatigue (2)
- Flying Spot Laser Thermography (2)
- Fourier transform (2)
- Heat diffusion (2)
- Impact (2)
- Impactschäden (2)
- In situ Monitoring (2)
- In-process monitoring (2)
- In-situ (2)
- Inter layer time (2)
- Iterative shrinkage thresholding algorithm (2)
- Laboratory specimens (2)
- Laser Beam Melting (2)
- Laser Powder Bed Fusion (PBF-LB/M, L-PBF) (2)
- Laser beam melting (2)
- Laser powderbed fusion (2)
- Laser-Pulver-Auftragschweißen (2)
- Laser-Thermografie (2)
- Laserauftragschweißen (2)
- MSG-Schweißen (2)
- Maintenance (2)
- Mechanochemistry (2)
- Metallanker (2)
- Moisture (2)
- Numerical simulation (2)
- Optical Tomography (2)
- Pitting corrosion (2)
- Polymerbeschichtungen auf Beton (2)
- Polymere (2)
- Pores (2)
- Porosity (2)
- Porosity prediction (2)
- Process Monitoring (2)
- Prozessmonitoring (2)
- Pulse-compression laser thermography (2)
- Robot path planning (2)
- Robot-assisted thermography (2)
- Roboter (2)
- Rotor blades (2)
- SWIR camera (2)
- Schichtdickenmessung (2)
- Schmelzbadbeobachtung (2)
- Schweißnahtgeometrie (2)
- Selective Laser Melting (SLM) (2)
- Standardization (2)
- Structured heating (2)
- Surface breaking defects (2)
- Surface cracks (2)
- Thermal effusivity (2)
- Thermal stress analysis (2)
- Time over threshold (2)
- Ultraschall (2)
- Wind turbine blade (2)
- Windenergie Anlage Rotorblätter (2)
- Windenergie anlage rotorblätter (2)
- thermografisches Verfahren (2)
- 1D-Simulation (1)
- 2D/3D thermographic registration (1)
- 3D imaging (1)
- 3d printing (1)
- ADMM (1)
- AGIL (1)
- AM (1)
- Absorptance (1)
- Absorption coefficient (1)
- Acoustic Emission (1)
- Active themrography (1)
- Additive Manufacturing (AM) (1)
- Afterglow (1)
- Ageing (1)
- Aktive Thermographie (1)
- Angle dependency (1)
- Anisotropy (1)
- Asphalt (1)
- Automated inspection system (1)
- Automatisierung (1)
- BPF-LB/M (1)
- Beständigkeit von Kunststoffen (1)
- Blind structured illumination (1)
- Block regularization (1)
- Block-sparsity (1)
- CT (1)
- Cellular substructure (1)
- Characterisation (1)
- Civil engineering (1)
- Classification (1)
- Co-axial monitoring (1)
- Complex shaped component testing (1)
- Computed tomography (1)
- Computed tomography (CT) (1)
- Computertomografie (1)
- Comressed Sensing (1)
- Contact area (1)
- Convolutional neural network (1)
- Convolutional neural networks (CNN) (1)
- Corrosion (1)
- Corrosion detection (1)
- Corrosion fatigue (1)
- Crack growth (1)
- Crack-detection algorithms (1)
- Damage detection (1)
- Data Fusion (1)
- Data fusion (1)
- Data processing (1)
- Debond (1)
- Deep imaging (1)
- Defect Prediction (1)
- Defect characterization (1)
- Defect identification (1)
- Defect prediction (1)
- Defektcharakterisierung (1)
- Defekte (1)
- Delamination depth (1)
- Delamination width (1)
- Delaminations (1)
- Diffusion (1)
- Digital micromirror device (1)
- Discharge arc (1)
- Dispersion (1)
- Dwell-time (1)
- Eddy-current testing (1)
- Effusivity (1)
- Electronic, optical and magnetic materials (1)
- Embedded sensors (1)
- Emissionsgrad (1)
- Emisssivity (1)
- Energieeintrag (1)
- Engineered barriers (1)
- Environment (1)
- Ettringite (1)
- FFF-3D printer (1)
- Fatigue crack growth rate (1)
- Fatigue testing (1)
- Fiber resisted polymers (1)
- Finite pulse length (1)
- Flash excitation (1)
- Flash lamp (1)
- Flaw detection (1)
- Flying line (1)
- Flying spot thermography (1)
- Gas dispersion simulation (1)
- General Chemical Engineering (1)
- General Chemistry (1)
- General energy (1)
- Haynes 282 (1)
- Heat source shape (1)
- Heißluftquelle (1)
- Heterogeneous (1)
- Heterogeneous materials (1)
- High temperature (1)
- High temperature alloys (1)
- Hot disc method (1)
- Hyperspectral (1)
- Hyperspectral Imaging (1)
- IR-Spektroskopie (1)
- IR-spectroscopy (1)
- Ideal delamination (1)
- Image reconstruction (1)
- Image registration (1)
- Imaging (1)
- Impact behaviour (1)
- In Memoriam (1)
- In situ (1)
- In situ NDE (1)
- In situ studies (1)
- In-situ Process Monitoring (1)
- In-situ process monitoring (1)
- Indoor air quality (1)
- Inverse Problem (1)
- Inverse problems (1)
- Iterative shrinkage thresholding (1)
- Keyhole porosity (1)
- Klebeverbindungen (1)
- LPA (1)
- LPBF (1)
- Lack-of-fusion (1)
- Laminates (1)
- Laminographie (1)
- Laplace transform (1)
- Laser Powder Bed Fusion (L-PBF) (1)
- Laser applications (1)
- Laser excitation (1)
- Laser heating (1)
- Laser line excitation (1)
- Laser powder bed fusion (PBF-LB/M, L-PBF) (1)
- Laser-Pulver-Auftragschweißen (LPA) (1)
- Laser-Pulverbettschweißen (1)
- Laserstrahlschmelzen im Pulverbett (1)
- Latin hypercube sampling (1)
- Layer thickness (1)
- Lock-in (1)
- Lock-in excitation (1)
- Lockin Thermografie (1)
- Luftultraschall (1)
- MWIR (1)
- Materials Characterization (1)
- Melt Pool (1)
- Melt pool depth (1)
- Melt-pool-monitoring (1)
- Metal (1)
- Metals (1)
- Micro-CT (1)
- Micro-computed tomography (1)
- Mid-IR absorption (1)
- Modeling (1)
- Modulated photothermal radiometry (1)
- Monitoring (1)
- Multi-dimensional reconstruction (1)
- Multispektral Thermografie (1)
- N-layers model (1)
- NIR (1)
- Neutron Diffraction (1)
- Nicht-lineare Regression (1)
- Non Destructive Testing (1)
- Non-destructive Materials (1)
- Non-destructive Testing (1)
- Nondestructive evaluation (1)
- Nondestructive testing (NDT) (1)
- Normierung (1)
- Oberflächenschutzsystem (OSS) (1)
- Oberflächenschutzsysteme (1)
- Obituary (1)
- Offshore monopile foundation (1)
- Offshore structures (1)
- Online Monitoring (1)
- Online Process Monitoring (1)
- Online monitoring (1)
- Onsite inspection (1)
- Optical Emission Spectroscopy (1)
- Optical emission spectroscopy (1)
- Optimization (1)
- Optische Emissionsspektroskopie (1)
- Optische Emissionsspektroskopie (OES) (1)
- Parker method (1)
- Passive IRT (1)
- Passve IR (1)
- Photoacoustic characterization (1)
- Photothermal Technique (1)
- Physical and theoretical chemistry (1)
- Physics-based deep learning (1)
- Polymers (1)
- Porositätsvorhersage (1)
- Post NDE (1)
- Post-processing (1)
- Potentiodynamic polarisation (1)
- Ppreheating temperature (1)
- Probabilistic analysis (1)
- Process development (1)
- Process parameter optimization (1)
- Process simulation (1)
- Pulse energy (1)
- Pulse shape (1)
- Pulse-compression (1)
- Pulverbettverfahren (1)
- Quality control (1)
- Qualitätsüberwachung (1)
- Quantification (1)
- Quantitative Temperatur (1)
- Raman spectroscopy (1)
- Real Temperature (1)
- Reflectivity (1)
- Regularization (1)
- Remote gas sensor model (1)
- Risserkennung (1)
- Robot (1)
- Robot‐assisted (1)
- SCF (1)
- SLM (1)
- SWIR (1)
- SWIR thermography (1)
- Safety (1)
- Schalenprüfstand (1)
- Schallemission (1)
- Schallemissionsanalyse (SEA) (1)
- Schmelzbadtemperatur (1)
- SealWasteSafe (1)
- Selective Laser Melting (1)
- Selective laser beam melting (1)
- Selective laser melting (1)
- Semi-transparent composite (1)
- Semitransparency (1)
- Semitrasnparent materials (1)
- Short crack (1)
- Single crystal superalloy (1)
- Spatiotemporal shaping (1)
- Spot-welded joints (1)
- Stainless Steel (1)
- Stainless steel (1)
- Standardisation (1)
- Structured illumination (1)
- Structured laser illumination (1)
- Strukturiert (1)
- Strukturierte Beleuchtung (1)
- Strukturiertes Heizen (1)
- Super resolution (SR) (1)
- Super-resolution imaging (1)
- Surfaces, coatings and films (1)
- TDLAS (1)
- TSA (1)
- TSRS optimization (1)
- Temperaturmessung (1)
- Temporal structuring (1)
- Texture mapping (1)
- Thermal Wave (1)
- Thermal Waves (1)
- Thermal analysis (1)
- Thermal contrast (1)
- Thermal diffusion (1)
- Thermal diffusivity (1)
- Thermal emission (1)
- Thermal engineering (1)
- Thermal excitation (1)
- Thermal percolation threshold (1)
- Thermal shock response (1)
- Thermal testing (1)
- Thermal wave field (1)
- Thermal waves (1)
- Thermische Simulation (1)
- Thermischer Kontakt (1)
- Thermocouple (1)
- Thermoelastic effect (1)
- Thermografie mit Stufenanregung (1)
- Thermograhy (1)
- Thermographic testing (1)
- Thermoplastic effect (1)
- Thickness determination (1)
- Thin film characterization (1)
- UV/VIS spectroscopy (1)
- Ultrafine particles (1)
- Ultrasonic imaging (1)
- Ultrasonic testing (1)
- Virtual wave concept (1)
- Virtual waves (1)
- Virtuelle Welle (1)
- Wavelet transformation (1)
- Welded (1)
- Wiederkehrende Prüfung (1)
- Wind rotor blade (1)
- Windenergie anlage rotorblätte (1)
- Windenergy (1)
- Windkraft (1)
- X-ray Diffraction (1)
- X-ray and Neutron Diffraction (1)
- X-ray computed tomography (XCT) (1)
- X-ray diffraction (1)
- XRD (1)
- ZFP4.0 (1)
- Zugprüfungen (1)
- additive manufacturing (1)
- automated thermographic nondestructive testing (1)
- infrared Thermography (1)
- inspection (1)
- photothermisch (1)
- super-resolution (1)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (292)
- 8.3 Thermografische Verfahren (292)
- 9 Komponentensicherheit (55)
- 9.3 Schweißtechnische Fertigungsverfahren (36)
- 8.5 Röntgenbildgebung (23)
- 9.6 Additive Fertigung metallischer Komponenten (22)
- 7 Bauwerkssicherheit (15)
- 8.4 Akustische und elektromagnetische Verfahren (13)
- 1 Analytische Chemie; Referenzmaterialien (12)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (12)
- 1.9 Chemische und optische Sensorik (10)
- 5 Werkstofftechnik (9)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (5)
- 9.4 Integrität von Schweißverbindungen (5)
- 4 Material und Umwelt (4)
- 5.4 Multimateriale Fertigungsprozesse (4)
- 4.2 Material-Mikrobiom Wechselwirkungen (3)
- 5.1 Mikrostruktur Design und Degradation (3)
- 2 Prozess- und Anlagensicherheit (2)
- 2.1 Sicherheit von Energieträgern (2)
- 5.0 Abteilungsleitung und andere (2)
- 6 Materialchemie (2)
- 6.3 Strukturanalytik (2)
- 1.4 Prozessanalytik (1)
- 1.6 Anorganische Referenzmaterialien (1)
- 4.5 Kunst- und Kulturgutanalyse (1)
- 5.2 Metallische Hochtemperaturwerkstoffe (1)
- 5.3 Polymere Verbundwerkstoffe (1)
- 7.1 Baustoffe (1)
- 7.2 Ingenieurbau (1)
- 7.4 Baustofftechnologie (1)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (1)
- 8.6 Faseroptische Sensorik (1)
- S Qualitätsinfrastruktur (1)
- S.0 Abteilungsleitung und andere (1)
Paper des Monats
- ja (3)
In the field of optically excited thermography, flash lamps (impulse shaped planar heating) and halogen lamps (modulated planar heating) have become established for the specific regimes of impulse and lock-in thermography. Flying-spot laser thermography is implemented by means of a rasterized focused laser, e. g. for crack detection (continuous wave operation) and photothermal material characterization (high-frequency modulated). The availability of novel technologies, i. e. fast and high-resolution IR cameras, brilliant innovative light sources and high-performance data acquisition and processing technology will enable a paradigm shift from stand-alone photothermal and thermographic techniques to uniform quantitative measurement and testing technology that is faster and more precise. Similar to an LED array, but with irradiance two orders of magnitude higher, a new type of brilliant laser source, i. e. the VCSEL array (vertical-cavity surface-emitting laser), is now available. This novel optical energy source eliminates the strong limitation to the temporal dynamics of established light sources and at the same time is spectrally clearly separated from the detection wavelength. It combines the fast temporal behavior of a diode laser with the high optical irradiance and the wide illumination area of flash lamps. In addition, heating can also be carried out in a structured manner, because individual areas of the VCSEL array can be controlled independently of each other. This new degree of freedom enables the development of completely new thermographic NDT methods.
Optical lock-in thermography is a completely contactless and very sensitive NDT technique. As an optical source of energy, incandescent lamps are most commonly used because they are relatively inexpensive and offer high irradiances at the test specimen. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowattclass laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration. We present current activities with kilowatt-class highpower laser sources for advanced lock-in thermography and focus on the application of laser arrays that offer a very high irradiation strength over a large sample area beyond the mentioned advantages.
Mit Laserlicht kann man eine Materialoberfläche berührungslos und schnell moduliert aufheizen. Dabei entsteht eine stark gedämpfte Wärmewelle, die tief ins Material eindringen kann. Erzeugt und überlagert man solche thermischen Wellen auf kohärente Weise, dann kann man damit versteckte Materialfehler zerstörungsfrei und sehr präzise aufspüren. Sogar eine bildgebende Tomografie ist denkbar.
Impact damages and delaminations in fibre-reinforced composites (FRC) might not be visible at the surface, but could have an influence on the resistance and on the long-term behaviour of the component. Therefore, and especially for safety relevant structures, non-destructive methods are required for the assessment of such damages.
Active thermography methods are suitable to characterize damages after loading using different kind of excitation techniques and various configurations of infrared (IR) camera and heating sources. Here, flash lamps, impulse excitation with infrared radiator and lock-in technique with halogen lamps or widened laser beams are suited. In addition, non-optical sources like sonotrodes (requiring direct contact to the structure) or induction generators (only suited for carbon fibre reinforced polymer (CFRP) structures) could be applied as well. For the investigation of the evolution of the damage during the impact, passive thermography can be applied in-situ. Elastic and plastic deformations alter the temperature of the structure and thus the temperature on the surface.
In this contribution, at first the general principles of quantitative defect characterisation in FRC using active thermography with flash, impulse and lock-in excitation are described. Optical and thermal properties of the FRC material and its anisotropy are considered. Results of phase differences obtained at flat bottom holes with flash and lock-in thermography are compared for qualifying both methods for quantitative defect characterization. Secondly, the damage evolution of CFRP and GFRP structures under impact load and static tensile loading is described. The spatial and temporal evolution of the surface temperature enables us to distinguish matrix cracks or fibre-matrix separation from delaminations between the layers. Afterwards, all results for loading defects, obtained by passive and active thermography, are compared with each other. Fig. 1 and 2 show the difference of passive and flash thermography obtained at impact and tensile loaded CFRP plates, respectively. As one purpose of these investigations is the development of standards within national (DIN) and European (CEN) standardisation bodies, new draft and final standards are presented and further needs are discussed at the end of the presentation.
In vielen Umgebungen, besonders bei hohen Temperaturen, korrosiven Umgebungen oder auf bewegten oder schlecht zugänglichen Flächen, kann die Temperatur nicht oder nur mit nicht akzeptablem Aufwand mit Berührungsthermometern gemessen werden. Diese Umgebungsbedingungen sind unter anderem in der chemischen Industrie, der Lebensmittel-, Metall-, Glas-, Kunststoff- und Papierherstellung sowie bei der Lacktrocknung anzutreffen. In diesen Bereichen kommen Strahlungsthermometer zum Einsatz. Der VDI-Statusreport zeigt typische Anwendungsfelder von nicht radiometrisch kalibrierten Wärmebildkameras und von radiometrisch kalibrierten Thermografiekameras. Um verlässlich mit spezifizierten Messunsicherheiten berührungslos Temperaturen zu messen, müssen die Strahlungsthermometer und Thermografiekameras nicht nur kalibriert, sondern radiometrisch und strahlungsthermometrisch umfassend charakterisiert werden. Auch die optische Materialeigenschaft, der spektrale Emissionsgrad und die Gesamtstrahlungsbilanz (Strahlung des Messobjekts und der Umgebung) sind bei der industriellen Temperaturmessung von großer Bedeutung. In den letzten Jahrzehnten ist dazu ein umfassendes technisches Regelwerk entstanden, das wir Ihnen mit diesem VDI-Statusreport vorstellen. Manche in den Richtlinien beschriebenen Kennwerte mögen abstrakt wirken. In diesem Statusreport zeigen wir an konkreten Beispielen, was diese Kenngrößen für die berührungslose Temperaturmessung bedeuten. Beispiele von Anwendungen zeigen, wo temperaturmessende Thermografiekameras und ausschließlich bildgebende Wärmebildkameras in der Praxis eingesetzt werden. Mit einer Analyse, welche Themen und Anwendungen derzeit besonders intensiv diskutiert werden, versuchen wir Trends für zukünftige Entwicklungen herauszuarbeiten.
Using spatial and temporal shaping of laser-induced diffuse thermal wave fields in thermography
(2020)
The diffuse nature of thermal waves is a fun-damental limitation in thermographic nonde-structive testing. In our studies we investigated different approaches by shaping the thermal wave fields which result from heating. We have used high-power laser sources to heat metallic samples. Using these spatial and temporal shaping techniques leads to a higher detection sensitivity in our measurements with the infra-red camera. In this contribution we show our implementation of shaping laser-induced diffuse thermal wave fields and the effect on the defect reconstruction quality.
Optical lock-in thermography is a completely contactless and very sensitive NDT technique. As an optical source of energy, incandescent lamps are most commonly used because they are relatively inexpensive and offer high irradiances at the test specimen. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowatt-class laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration.
We present current activities with kilowatt-class high-power laser sources for advanced lock-in thermography and focus on the application of laser arrays that offer a very high irradiation strength over a large sample area beyond the mentioned advantages.
Optical lock-in thermography is a completely contactless and very sensitive NDT technique. As an optical source of energy, incandescent (i.e. halogen) lamps are most commonly used because they are relatively inexpensive and offer high irradiances at the test site. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowatt-class laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz, see Fig.1. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration.
Using the one-dimensional solution to the thermal heat diffusion equation together with the absorptance of the material which is illuminated with a harmonically modulated light source, we can calculate the temperature oscillation at the surface of a solid. As a second step, we calculate the corresponding oscillation of the total thermal emission using Stefan-Boltzmann law as a first order approximation and taking into account the emissivity of the material. Within this framework we can calculate the minimal irradiance of a light source necessary to provoke a measurable signal within a thermographic camera at a noise equivalent temperature difference (NETD) of 30 mK. In Fig. 2 this relationship is displayed for a wide spectrum of modulation frequencies and for a number of different light sources scaled to the same electrical input power and illumination area. Using this figure, it is now easily possible to analyze the range of materials to be tested using lock-in thermography, since only the materials (dotted lines) below the irradiance-vs-frequency curves (solid lines) are heated in excess of the camera’s NETD. This figure clearly shows that laser sources considerably increase the application range of lock-in thermography, since especially for metals with a high reflectance and high thermal diffusivity a high irradiance is vitally important to allow for lock-in texting.
We present current activities with kilowatt-class high-power laser sources for advanced lock-in thermography and focus on the application of laser arrays that offer a very high irradiation strength over a large sample area beyond the mentioned advantages.
Optical lock-in thermography is a completely contactless and very sensitive NDT technique. As an optical source of energy, incandescent (i.e. halogen) lamps are most commonly used because they are relatively inexpensive and offer high irradiances at the test site. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowatt-class laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz, see Fig.1. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration.
Using the one-dimensional solution to the thermal heat diffusion equation together with the absorptance of the material which is illuminated with a harmonically modulated light source, we can calculate the temperature oscillation at the surface of a solid. As a second step, we calculate the corresponding oscillation of the total thermal emission using Stefan-Boltzmann law as a first order approximation and taking into account the emissivity of the material. Within this framework we can calculate the minimal irradiance of a light source necessary to provoke a measurable signal within a thermographic camera at a noise equivalent temperature difference (NETD) of 30 mK. In Fig. 2 this relationship is displayed for a wide spectrum of modulation frequencies and for a number of different light sources scaled to the same electrical input power and illumination area. Using this figure, it is now easily possible to analyze the range of materials to be tested using lock-in thermography, since only the materials (dotted lines) below the irradiance-vs-frequency curves (solid lines) are heated in excess of the camera’s NETD. This figure clearly shows that laser sources considerably increase the application range of lock-in thermography, since especially for metals with a high reflectance and high thermal diffusivity a high irradiance is vitally important to allow for lock-in texting.
We present current activities with kilowatt-class high-power laser sources for advanced lock-in thermography and focus on the application of laser arrays that offer a very high irradiation strength over a large sample area beyond the mentioned advantages.
Optical lock-in thermography is a completely contactless and very sensitive NDE technique. As an optical source of energy, incandescent (i.e. halogen) lamps are most commonly used because they are relatively inexpensive, do not need any work safety measures and offer high irradiances at the test site. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowatt-class laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration. Altogether using lasers considerably increases the application range of lock-in thermography, since especially for metals with a high reflectance and high thermal diffusivity a high irradiance is vitally important to allow for lock-in testing [1, 2]. We report on the mentioned benefits of using such high-power lasers and analyze the range of materials to be tested using lock-in thermography in dependence on the laser irradiance, the modulation frequency, the infrared camera as well as the optical and thermal material parameters. In this context, we also address a number of systematic errors caused by the use of ideal and non-ideal heat sources. For example, the measured phase angle in lock-in thermography depends on the irradiance and the modulation bandwidth of the source. This in turn has a decisive influence on the uncertainty in the quantification of, e.g. layer thicknesses.